The present invention relates to a tank ventilation valve, to a tank ventilation system for a motor vehicle and to a method for keeping open an electromagnetically actuated valve of the normally closed type.
In motor vehicles, fuel vapors from a fuel tank are to be retained by a vent line to the atmosphere being closed by a valve during motor standstill and being opened only during operation of the engine, so that by the removal of fuel, air can enter the tank to prevent negative pressure in the tank. In addition, an activated carbon canister is provided in the vent line to absorb fuel vapors therein. During operation of the engine, the activated carbon canister is regenerated by drawing combustion air from the engine through the activated carbon filter.
Before a fuel cap is opened, the vent line must be opened to relieve any overpressure in the fuel tank in order to prevent fuel from spurting out of the open fuel cap. Furthermore, the vent line must be opened for refueling the fuel tank, so that the displaced air can escape through the vent line and spurting out of fuel from the open tank cap is prevented.
For this purpose, an electromagnetically actuated on/off valve is arranged in the vent line, which is normally closed and can be opened by corresponding activation of an electromagnet. Such valves are disclosed for example in DE 10 2010 044 336 A1 and DE 10 2011 114 120 A1.
During assembly line production of motor vehicles, a certain minimum amount of fuel must be filled into the fuel tank, so that a final inspection of the vehicle can be carried out and the vehicle can be moved independently after completion. Here, the vent valve of the fuel tank must be energized to open the vent line. However, a fully operational electrical control may not be available and ready for use during assembly line production. Therefore, to open the tank ventilation valve, the tank ventilation valve must be opened externally with a corresponding special control to refuel the vehicle that has not been finished yet. Such a procedure is cumbersome and takes a long time, so that the entire assembly line production is delayed thereby.